Definition

May occur together or separately. Urticaria involves only the superficial dermis and presents as pruritic, circumscribed wheals with raised serpiginous borders and blanched centers. Angioedema involves deeper layers of skin and may include subcutaneous tissue; it is marked by dramatic swelling with more pain than pruritus. Recurrent episodes of urticaria and/or angioedema of <6 weeks duration are considered acute, whereas attacks persisting beyond this period are chronic.

Classification, Etiology, and Pathophysiology

The classification of urticaria-angioedema focuses on mechanisms that elicit clinical disease and can be useful for differential diagnosis (Table 159-1 Classification of Urticaria and/or Angioedema). Acute urticaria is most often the result of exposure to a food, environmental or drug allergen or viral infection. Chronic urticaria is often idiopathic with additional etiologies including physical stimuli. Up to 45% of pts with chronic urticaria have an autoimmune cause including autoantibodies to IgE or to the α chain of FcεRI. Hereditary angioedema (HAE) is a fully penetrant, autosomal dominant disease due to a mutation in the SERPING1 gene leading to a deficiency of C1 inhibitor (C1INH) (type 1-85% of pts) or to a dysfunctional protein (type 2).

Diagnosis

History, with special attention to possible offending exposures and/or ingestion as well as the duration of lesions. Urticarial eruptions appear in crops of 12- to 36-h duration, with old lesions fading as new ones appear. In physical urticarias, individual lesions usually last <2 h. Lesions that last >36 h, result in scarring, and are painful rather than pruritic warrant skin biopsy for urticarial vasculitis. The most common sites for angioedema are periorbital and perioral; upper respiratory tract angioedema may be life-threatening. HAE is suggested by family history, lack of pruritus or urticarial lesions, GI involvement with attacks of colic, and episodes of laryngeal edema.

• Skin testing to food and/or inhalant antigens
• Direct reproduction of the lesion in physical urticaria
• Laboratory examination: CBC with differential (eosinophilia), TSH, erythrocyte sedimentation rate (ESR) are recommended. C1INH and complement levels if HAE is suggested. Expanded testing should be guided by history: assay for serum allergen-specific IgE, mast cell studies, cryoglobulins, hepatitis testing, autoantibody screen.
• Skin biopsy may be necessary.

Differential Diagnosis

Atopic dermatitis, contact sensitivity, cutaneous mastocytosis (urticaria pigmentosa), systemic mastocytosis.

Prevention

Identification and avoidance of offending agent(s), if possible.